Bassily, A. M., 1999, xe2x80x9cImproving the Efficiency and Availability Analysis of a Modified Reheat Regenerative Rankine Cyclexe2x80x9d Proceedings of the Renewable and Advanced Energy Systems for the 21st Century, Lahaina, Maui, Ha. April 11-15.
Moran, M. J., and Shapiro, H. N., 1995, Fundamentals of Engineering Thermodynamics, John Wiley and Sons, Inc., New York, 3rd Edition, pp. 590-610.
The present invention relates to the field of power generation system of the continuous combustion type using steam as the working medium. The general objective of the invention is to provide a system of power generation, having higher efficiency than the current systems while maintaining low capital cost, leading to a total running cost that is lower than the total running cost of the existing systems.
Increasing the efficiency of power generation can be done by increasing the average temperature of heat reception through regeneration or reheating. The main purpose of reheating is to ensure high efficiency of expansion through steam turbines. The average temperature of heat reception can be increased through raising the steam generator pressure (Px). As Px increases, there will be need for more stages of reheating to ensure high efficiency of expansion in steam turbines. As the number of reheating stages grows, more steam will be extracted for regeneration at high superheat temperature that has high temperature difference of heat transfer. Such a high temperature difference of heat transfer increases the irreversibility of feed water heaters. There is no feasible method is known to reduce the irreversibility of feed water heaters in case of using superheated steam for feed heating. This invention introduces some modifications to the Rankine Reheat Regenerative cycles that reduce the regeneration irreversibility and increase the cycle efficiency.
The invention is particularly advantageous for use in systems that use steam as a working medium; however, the invention is also advantageous for power systems that use any other fluids as working media. The invention can also be applied to the combined cycle power systems and Binary cycle power systems.
In general, it may be said that I attain the principal object of the invention, as well as the other objects thereof which will hereinafter appear, by further expanding the required amount of the working medium to be reheated just for the purpose of further expanding it in rotary turbines to produce power. The required amount of the working medium to heat the fluid entering each feed heater is extracted at almost the same pressure that corresponds to that heater. The remainder amount of that required for feed generation of the working medium after expansion if it is in a two-phase condition is allowed to enter a separator to convert the inlet two phase of the working medium to two outlets. The first outlet is dry gas and the second outlet is liquid. The dry gas will either be reheated to higher temperature just for the purpose of effective expansion in the following stage of expansion in a rotary turbine, or will be allowed to expand in the following stage of expansion without reheating. The liquid working medium out of the separator will mix with the outlet of that feed heater. If the remainder amount of that required for feed regeneration after expansion was in a gas phase condition, it is allowed to expand further in the same rotary turbine to the pressure that equal to the pressure of the next feed heater. By this process, I am enable to use working medium in a two-phase region to heat the feed heater at a pressure that is almost equal to the pressure of that heater, resulting:
First, a reduction in the feed water heater irreversibility since the temperature difference of heat transfer is minimum, resulting in a higher efficiency for the power system.
Second, a higher heat transfer coefficient since the heat transfer coefficient of the condensing two-phase working medium used to heat the working medium entering feed heater is up to 200 times that of a gas-phase working medium, resulting in a smaller and cheaper heat exchange units for feed generation.
Third, the amount of working medium that is expanded further for the purpose of power generation is reduced significantly. The results show that up to 50% reduction in the mass flow rate of the reheater pipes of the invented cycle over the regular current Rankine reheat regenerative cycle at the same conditions of temperatures, pressures, number of feed water heaters, and reheating stages. Such results lead to up to 75% reduction in the pressure drop of the reheater pipes and significant reductions in the heat transfer losses from such pipes (assuming the same pipe sizes and coefficients of friction), resulting in further improvement in thermal efficiency.
Therefore, implementing the invention is expected to reduce the capital cost of the equipment and the cost of energy to run it, resulting in a reduction of the total cost. The invention is applicable to many different arrangements of power systems and for the purpose of illustration I have shown in the accompanying drawing several schematic diagrams for carrying the invention into effect, together with the corresponding illustrations of the thermal characteristics of those cycles.
In the systems illustrated, the working medium is water in the liquid phase, steam in the gas phase. Any kind of fuel can be applied to those systems such as fossil fuel (oil, natural gas, coal), nuclear fuel. For convenience, I will refer, but without limitation to the working fluid as water in a liquid form and steam in a gas form. It is understood that other media having equivalent functions may be employed instead.